In recent years, intelligent materials have been attracting attention. An intelligent material refers to a material which exhibits its function in response to an external stimulus such as temperature, pH, or body fluid. Typical intelligent materials are exemplified by a drug delivery system, a self healing material and the like.
In order to provide an intelligent function to a sheet-like structure such as a nonwoven fabric, there are effective methods, for example, a method of applying porous microcapsules having a functional component encapsulated therein, and a method of pasting a film containing a functional component. Provided with an intelligent function responsive to an external stimulus, a sheet-like structure can be a functional material which is capable of exhibiting its maximum function when needed and of protecting the functional component until being used.
At present, an integration of an intelligent material and a sheet-like structure is generally performed by a coating method using a binder. However, with the coating method using a binder, the binder covers the surfaces of the microcapsules and the film, so that the intelligent material loses a function responsive to an external stimulus, the function being unique to the intelligent material. Therefore, the coating method using a binder is not suitable for the integration of a functional material containing a functional component and a sheet-like structure such as a nonwoven fabric.
Here, Japanese Patent No. 2728298 (Patent Document 1), Japanese Patent No. 2728299 (Patent Document 2), Japanese Patent No. 2862275 (Patent Document 3), and Japanese Patent No. 2940930 (Patent Document 4) describe methods for producing a hydrated alginic acid film by utilizing such a property of a soluble alginate that the soluble alginate can easily be gelatinized by reaction thereof in an aqueous solution with a divalent metal salt such as a salt containing calcium ion. The hydrated alginic acid film can be applied to external preparations such as medicines, and cosmetics, and is capable of containing an appropriate functional component such as a moisture retention agent, a sanitizer or the like, in accordance its application.
However, the film obtained by any of the methods described in the foregoing Patent Documents 1 to 4 is a hydrated film. Accordingly, when used as a sanitary product, which is used in constant contact with a skin, the film releases the functional component by simply being applied with an external pressure without being in contact with a body fluid such as sweat. Thus, it is impossible to render the release of the functional component body-fluid responsive.